Scuba-diving mouthpieces of various kinds have been known and used for many years. The great majority of such mouthpieces are not customizable for individual divers, but some customizable scuba-diving mouthpieces have been known or used. Examples of customized or customizable scuba-diving mouthpieces are those shown in U.S. Pat. Nos. 3,107,667 (Moore), 3,844,281 (Shamlian), 3,929,548 (Shamlian), and 4,136,689 (Shamlian).
Despite advances in recent years, there are many problems and shortcomings with scuba-diving mouthpieces of the prior art. One fairly common problem relates to mouth fatigue experience by scuba divers. Mouthpieces are typically held in place by means of the diver's bite on retaining members which project inwardly from a lip-engaging portion to positions between the upper and lower teeth. This not only places significant pressures on small portions of the diver's teeth, that is, the portions engaging the retaining members, but the constant muscle pressure needed for secure retention of such mouthpieces can cause significant muscle strain and aching.
Customizing the surfaces of such retaining members to match the tooth surfaces, as in the above-mentioned Shamlian patents, ameliorates the problem to some extent. However, the improvement is very limited because of the fact that contact with the inwardly-projecting retaining members is limited to only a few teeth.
Greater tooth contact is possible with scuba-diving mouthpieces such as the customized mouthpiece disclosed in the above-mentioned Moore patent. The tooth-engaging portions in such device extend well back along the line of molars on either side of the mouth. Such extension provides a greater lever arm, thereby reducing the pressure necessary to hold the mouthpiece in the mouth. Because of this, mouth fatigue should be reduced. However, the process used to manufacture such mouthpiece is extremely complex, requiring steps such as making wax replicas of the maxillary and mandibular impressions of the mouth, mounting such replicas in the appropriate relative positions of the partly-opened mouth, carving, uniting tube and tooth impression portions, plaster forming, introducing vulcanizable rubber, separating plaster from formed rubber, and other steps.
The complexity of this manufacturing process rules out quick preparation, such as in a diving equipment shop. Furthermore, it can produce mouthpieces which are less than satisfactory in comfort. In some cases, this is because the relative positions of the relative maxillary and mandibular portions may not be natural. In other cases, this may be because the relative positions are not sufficiently closed. The problem of unnatural jaw position placement is accentuated for the 20% or so of the population whose jaws are developed well away from normal patterns. In each case, improper relative placement, even in customized scuba-diving mouthpieces, exacerbates the usual problems of jaw fatigue.
The problems of jaw fatigue and joint strain during long use are accompanied by a related problem--a tendency toward an inability by the diver to easily maintain the mouthpiece in the proper orientation, particularly when pressures are applied to the mouthpiece from outside the diver's mouth. Unwanted pressures on the mouthpiece grip come about from water currents (relative to the diver), contacts made with diving apparatus, and a variety of other causes. It is essential, of course, that the diver's mouthpiece, which is the sole source of air, remain in place. Thus, the concern about pressure interfering with the grip of the diver on his or her mouthpiece is more than a casual concern.
Some problems with current scuba-diver mouthpieces can be understood better by reference to the mouth, the jaw, and the teeth of a typical person. The jawbone is a lengthy angled member which pivots with respect to the skull about the jaw joint well back from the mouth. Such joint is typically positioned considerably above the level of the teeth and well behind the position of the teeth. From such joint, the jaw has a generally downwardly and slightly forwardly extending portion which extends generally to a position rearwardly spaced from the teeth, and a more forwardly, but still downwardly, extending portion which carries the teeth of the lower jaw and extends forwardly beneath the upper jaw. The angle between the two portions of the lower jaw is referred to herein as the "jaw angle."
Opening and closing muscle tissue masses are secured to the jaw at positions forward of the jaw joint, but well rearward of the teeth. The muscles secured to the lower jaw create a lever arm which extends from the jaw joint all the way to the point of contact pressure of the lower jaw with the upper jaw or with whatever is being bitten.
When using a typical diving mouthpiece, or a customized diving mouthpiece such as those shown in the aforementioned Shamlian patents, the lever arm of the lower jaw extends from the jaw joint all the way forward to the position of the eye teeth where the mouthpieces are gripped between the diver's teeth.
Two separate problems are created when the mouthpiece contact occurs in this manner at such forward position in the mouth: First, since the distance from the center of muscle effort is long, a significant increase in muscle force is necessary to stabilize and retain the mouthpiece. This is what causes the muscles to quickly fatigue and often to become painful, which leads to jaw aches and headaches. A second and related problem of such long lever arm is created when standard mouthpieces, or customized mouthpieces of the Shamlian type are used, in that there is a severe increase in pressure within the jaw joint, well back in the head.
If the contact location is extended to the back of the mouth, the lever arm is shortened and advantages are achieved, including a reduction in the muscle force necessary to hold the mouthpiece and a reduction in the corresponding jaw pressure. Lengthening the mouthpiece retention piece to allow contact at a more rearward position in the mouth creates a shorter, and thus more favorable, lever arm. This resists torque from movement of the diver's regulator. That is, a better grip can be maintained with less exertion.
However, extension of the posterior bite pieces has been difficult or unworkable in the prior art due to variability in the jaw alignment of different people. Only a completely customized bite portion would allow for this. The variability in the angle between the teeth of the upper and lower jaws is a major problem. Such variability is caused by variations in the aforementioned lower jaw angle and also by the angle of the upper jaw with respect to the lower jaw. The upper jaw may be tipped up or down in the front or back.
Another major problem with previous customizable mouthpieces is caused by the extreme variability of the front teeth (incisors) in their generally vertical direction relative to the back teeth. When these teeth extend downwardly more than the average distance, they tend to partially the cover the air intake of the mouthpiece. When the diver bites on the bite portions, this creates a partial reduction in air flow and increased turbulence. The diver tends to experience "starving" for air in this circumstance. Mouthpieces of the prior art have maintained the lower front flange of the mouthpiece at a position vertically directly below the upper flange. However, when the typical jaw opens it follows a variable path that is down and back. At a position 4-6 cms open, which is the average mouth opening for a diving mouthpiece, the lower jaw typically must come forward to grip the bite portions and seal against the lower front flange. This tends to cause significant muscle strain, and places the jaw joint in an unnatural position, with a heavy load on it.
Known customizable scuba-diving mouthpieces have been unable to easily and properly accommodate a wide variety of mouth and tooth configurations. It would be desirable to have a customizable scuba-diving mouthpiece which can provide excellent and easy diver engagement for a wide variety of divers.
There are other problems related to creation of a totally customizable scuba-diving mouthpiece. With broad-reaching customizability there come problems in maintaining strength and integrity in the mouthpiece, at points of pressure and torque. For example, materials which are both readily thermoformable and of acceptable flexibility may be weakened by torque applied at certain points. More specifically, a torque applied on the mouthpiece can cause tearing of such material unless mouthpiece construction and design are such as to minimize or rule out such risk of damage. Furthermore, it is necessary that customizing of critical surfaces of such a mouthpiece be carried out without degrading the structural integrity and strength of the mouthpiece.
Still another concern with customized scuba-diving mouthpieces of the prior art is that such mouthpieces do not very well accommodate what is referred to by divers as "buddy-breathing." Buddy-breathing involves use of a single mouthpiece by more than one diver, as may be necessary when the oxygen supply of one diver is low. In such situations, the mouthpiece is handed back and forth for alternating use by two divers. Customized mouthpieces of the prior art are not well suited for this practice. This is particularly true for mouthpieces having extended tooth engagement along either side of the diver's mouth.
Problems in manufacture can arise in the final customizing steps, that is, in fitting a customizable scuba-diving mouthpiece for a particular diver. While it is desirable to have a large area of customized tooth mouthpiece engagement, heating of the mouthpiece could lead to unacceptable deformation in areas not to be engaged by the mouth, for example, areas to engage the air conduit of a second-stage regulator. It would be desirable to have a customizable mouthpiece not susceptible to such problems.
While there have been a number of efforts to make improved customizable scuba-diving mouthpieces, there has remained a clear need for significant improvements in the field of customizable scuba-diving mouthpieces.